Synthesis and mass spectral characterization of poly(amic methyl ester) oligomers

A series of monodisperse oligomers of poly(amic methyl ester) were synthesized by a stepwise, convergent-divergent strategy, starting from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA). All of the fully protected, selectively protected, and nonprotected oligomers were studied by MALDI mass spectrometry. The oligomers with protected end groups proved to be stable during MALDI ionization and the possibility of imidization as the result of synthesis or during MALDI experiments was discounted based on mass spectra of imide analogue oligmers. The effect of end groups and oligomer length on the MALDI ionization efficiency was determined. Higher molecular weight oligomers had more intense fragment peaks. MALDI-CID was used to examine the fragmentation patterns of selected oligomers. It was found that the end groups affected the fragmentation of the oligomers. The use of different CID gases ( helium, argon, and xenon) had no effect on the fragmentation pattern, but xenon caused more intense fragment peaks in the CID spectra.